Bhg???? Over heating maybe head gasket? Thermo?

[AlexSchuSupra]

I have been having a heating problem with my 87 5 spd NA. When I bought the car I took it to get the radiator flushed with chemicals and the water pump and thermo were replaced. This car ran absolutley cool! Never even went close to the halfway line. Anyway lately the hot/cold gauge had been freaking out on me. One minute it will jump way past the hot line and then drop back down to normal. It gets worse on long drives in will lean on the hot side alot more. Well today on my 90 mile drive I was shooting BOILING coolant out of the resevoir. Normally this scares me especially when my gauge is past the hot mark but I don't think it is a BHG. PLEASE! haha. Ok so I lifted the hood up and yep sure enough the coolant is spraying out the resevoir at boiling point. whats funny is the engine is not hot..... at least not that I can tell..... no excessive heat when the hood come up and I can even touch the motor for a bit. WHAT THE HELL???? I have no milky oil or any funny colored smoke or anything. Just the freaking coolant spraying out. I just want to know if you think it is a BHG cause if it us that sure blows!!!!!!!!! Maybe thermo again? Hoses? Rad. cap? Thanks guys!